studies regarding the influence of the ultrasonication conditions … · 2015-05-26 · with edax...

Abstract—The influence of the ultrasonication conditions

(time and amplitude of ultrasonication) upon the adsorptive

properties of the obtained ionic liquid impregnated material, in

the removal process of Cs+ ions from aqueous solutions, was

studied. In the last years ionic liquids was used for the

treatment of waste waters containing radionuclides. In order to

minimize the treatment cost and to enhance the treatment

efficiency, as an alternative to liquid-liquid extraction processes,

the use of ionic liquid impregnated support was proposed as a

new concept. In the present paper the ultrasonication was used

for the impregnation of 1-Butyl-3-methylimidazolium

hexafluorophosphate-[BmimPF6] onto Florisil support.

Different physical-chemical analysis (scanning electron

microscopy (SEM), energy dispersive XRay analysis (EDX),

and FTIR- Fourier transform infrared spectroscopy) was used

to characterize the obtained ionic liquid impregnated material.

In order to obtain a stable and homogenous impregnation of the

solid support surface with the studied ionic liquid which will

achieve reproducible results in the Cs+ adsorption processes it is

not necessary to increase the ultrasonication time, but it should

be used higher amplitude. The adsorption performance of the

Florisil impregnated with [BmimPF6], using optimum

conditions of ultrasonication, was studied as a function of Cs+

ions initial concentrations. Adsorption isotherms like Langmuir,

Freundlich, Dubinin–Radushkevich (D–R), and Temkin were

used to analyze the equilibrium data at different concentrations.

The experimental data showed good fit to the Langmuir

isotherm, followed by the Temkin and Dubinin-Radushkevich

isotherms and then the least fit was obtained with the

Freundlich isotherm.

Index Terms—Cs+ adsorption, impregnation, ionic liquid,

ultrasonication.

I. INTRODUCTION

The disposal of radioactive wastes is an issue relevant to

almost all countries, therefore the studies regarding the

removal of radioactive isotope from aqueous solutions are

growing continually [1]-[4]. In recent years, ionic liquids

(ILs) have gained a considerable attention and a choice to

replace the volatile organic compounds (VOCs) in solvent

extraction, due to their high thermal stability, very low

flammability and negligible vapor pressure [5]-[11].

Therefore the researchers focused on the developing of

another class of sorptive material through impregnation of

various ionic liquid onto different solid support [10]-[13].

Manuscript received December 15, 2014; revised March 19, 2015.

The authors are with the University Politehnica Timisoara, Faculty of

Industrial Chemistry and Environmental Engineering, Blvd. V. Parvan, no.6,

300223, Timisoara, Romania (e-mail: [email protected]).

Studies Regarding the Influence of the Ultrasonication

Conditions on the Adsorption Performance of Obtained

Ionic Liquid Impregnated Materials

L. Lupa, A. Negrea, M. Ciopec, R. Vodă, and P. Negrea

International Journal of Chemical Engineering and Applications, Vol. 6, No. 6, December 2015

410DOI: 10.7763/IJCEA.2015.V6.520

Compared with liquid-liquid extraction, solid-liquid

extraction provides an effective method for ILs application in

separation. In this way a higher efficiency in the removal

process of metals ions from aqueous solutions is obtained,

because it took the advantages of the chemical functionality

that ILs can impart and the properties of the solid support

[10], [12]-[17]. Different methods of extractant impregnation

onto various solid supports have been published such as: dry

method of impregnation, encapsulation, sol-gel method,

chemical immobilization [6], [7], [9], [11], [12], [18]-[22].

All these mentioned methods are quite time consuming;

therefore an alternative green and economic process

involving ultrasonication for the impregnation of the metal

extractant was proposed [23], [24]. So far, there are no

reports about the influence of the work condition of

ultrasonication method upon the adsorbent properties of the

obtained ionic liquid impregnated material. Therefore in the

present paper was study the influence of the work condition

of ultrasionication method upon the adsorption performance

of the Florisil impregnated with 1-Butyl-3-

methylimidazolium hexafluorophosphate-[BmimPF6]. This

ionic liquid was chosen because the imidazolium based ionic

liquids were intensive investigated in literature and showed

higher stability [25]-[27]. An inorganic solid support was

used due to highly porous texture and large specific surface

area. The obtained Florisil impregnated with [BmimPF6] at

various work conditions of ultrasonication was subjected to a

complex characterization scanning electron microscopy

(SEM), energy dispersive XRay analysis (EDX), and Fourier

transform infrared spectroscopy (FTIR). In order to

determine the influence of the impregnation work condition

upon the adsorbtive performance of the obtained material it

was used in the removal process of Cs+ ions from aqueous

solutions.

II. EXPERIMENTAL

For the impregnation of the Florisil with the [BmimPF6] IL

the time of ultrasonication (10-60 minutes) and the amplitude

(10-100%) using a Sonorex Super 10P ultrasonic bath, was

varied. In all the experiments the ratio between the ionic

liquid and solid support was kept at 0.1:1. Scanning Electron

Microscopy (SEM) was used in order to investigate the

changes of the surface morphology of the obtained adsorbent

function of the impregnation conditions. SEM images were

recorded using a Quanta FEG 250 Microscope, equipped

with EDAX ZAF quantifier. The FTIR spectra (KBr pellets)

of the obtained materials were recorded on a Shimadzu

mailto:[email protected]


411

Prestige- 21 FTIR spectrophotometer in the range 4000–400

cm-1. In order to establish the optimum conditions of

impregnation, 0.1 g of obtained materials were treated with

25 mL of 10 mg/L Cs+ ions solutions, obtaining the

dependence of the Cs+ ions uptake versus the ultrasonication

time and amplitude. In these experiments the samples were

stirred for 1 h using a Julabo SW23 shaker. After the time

elapsed the samples were filtered and the residual

concentration of Cs+ ions was analyzed through atomic

emission spectrometry using a Varian SpectrAA 280 type

atomic absorption spectrometer using air/acetylene flame.

The Cs+ ions uptake was expressed using (1):

m

VCCq e

e

0 (1)

where: C0 and Ce are the concentrations of Cs+ ions (mg/L) in

the solution initially (t 0) and at equilibrium, respectively, V

is the volume of the solution and m is the mass of adsorbent.

For the Florisil impregnated with [BmimPF6] in the

recommended conditions established in the first step of the

research, the maximum adsorption capacity in the removal

process of Cs+ ions from aqueous solutions was determined.

In this aim the dependence of the Cs+ ions uptake was

determined varying the initial concentrations of Cs+ ions

from aqueous solutions (range 5-50 mg/L). Adsorption

isotherms like Langmuir, Freundlich,

Dubinin–Radushkevich (D–R), and Temkin were used to

analyze the equilibrium data at different concentrations.

The linearized form of the Langmuir equation is given in

(2) [9], [14], [19], [24]:

m

e

mLe

e

q

C

qKq

C

1 (2)

where qm is the maximum adsorption capacity for a

monolayer coverage, KL is a coefficient related to the affinity

between the adsorbent and the adsorbate.

The linear form of the Freundlich isotherm equation is

expressed in (3) [9], [14], [19], [24]:

eFe C

nKq ln

1lnln (3)

where KF is a constant describing the adsorption capacity

(L/mg) and 1/n is an empirical parameter related to the

adsorption intensity.

In (4) is given the linear form of Temkin isotherm model

[19], [28]:

e

T

T

T

e Cb

RTK

b

RTq lnln (4)

where RT/bT in (J/mol) corresponding to the heat of

adsorption R is the ideal gas constant, T(K) is the absolute

temperature, bT is the Temkins isotherm constant.

The linear form of the D-R isotherm is given in (5) [28]:

2

11lnlnln

e

ddeC

RTBqq (5)

The apparent energy of adsorption, E was calculated using

(6):

22

1

dBE (6)

The constant qd (mol/g) is the D-R constant representing

the theoretical saturation capacity and Bd (mol2/J2) is a

constant related to the mean free energy of adsorption per

mole of the adsorbate, R is the ideal gas constant,

(8.314J/molK), T(K) is the temperature of adsorption, and

E(kJ/mol) is the mean free energy of adsorption per molecule

of the adsorbate when transferred to the surface of the solid

from infinity in solution.

III. RESULTS AND DISCUSSION

A. Characterization of the Impregnated Florisil with

[BmimPF6] Using Various Conditions of Ultrasonication

The morphology of the [BmimPF6] impregnated onto

Florisil using various time of ultrasonication at amplitude of

100% is shown in Fig. 1.

10 min 20 min 30 min

40 min 50 min 60 min

Fig. 1. SEM images of Florisil impregnated with [BmimPF6] using various ultrasonication time.


412

It can be observed that the increasing of the ultrasonication

time lead to a patchy conglomeration of the studied IL onto

the surface of Florisil support. The most uniform adherence

of the IL particle onto the Florisil is obtained in case of 10

minutes of impregnation. Also at this time the adherence is

deeper in the particles of the solid support, in this way the

leaching of the IL from the solid support surface during the

adsorption experiments is avoided. These results are

significant in order to obtain reproducibility of the Cs+

adsorption process.

The intensity of sonication is proportional to the amplitude

of vibration of the ultrasonic source and, as such, an

increment in the amplitude of vibration will lead to an

increase in the intensity of vibration and to an increase in the

sonochemical effects. In our case the increasing of the

amplitude lead to an increase in the IL quantity which is

impregnated onto the Florisil surface.

10% 30% 50%

70% 100%

Fig. 2. SEM images of Florisil impregnated with [BmimPF6] using various

ultrasonication amplitude.

From the SEM images of the materials obtained using

various amplitude of ultrasionication for 10 minutes (Fig. 2)

it can be observed that through the amplitude increasing is

achieved an easier transmission of the IL particles through

the liquid media until reach the cavities of the solid support.

The phenomenon indicates that [BmimPF6] did not coat on

the surface of Florisil, while existed in the inner when

amplitude of 100% is used for the impregnation through

ultrasonication. This assures a higher stability of

impregnation, avoiding the loss of IL from the surface of

Florisil.

TABLE I: THE QUANTIFICATION OF P, F, AND N FOR THE OBTAINED

IMPREGNATED MATERIALS RESULTED AT EDX ANALYSIS

Time of

ultrasoni-

-cation

P,

wt %

F,

wt %

N,

wt %

Amplitude of

ultrasoni-

-cation

P,

wt %

F,

wt %

N,

wt %

10 min 1.64 0.13 2.21 10 % 0.59 0.03 1.19

20 min 0.57 0.06 1.53 30% 0.62 0.03 1.21

30 min 0.64 0.05 1.48 50% 0.62 0.06 1.26

40 min 1.23 0.06 1.15 70% 1.52 0.09 2.17

50 min 1.08 0.05 0.91 100% 1.64 0.13 2.21

60 min 1.65 0.04 2.19

In order to approve that the Florisil was impregnated with

the studied ionic liquid, the obtained material were also

subject to the EDX analyze. In Table I are presented the

quantifications of P, F, and N (specific elements from the

ionic liquid which appear on the solid support due to the

impregnation).

It can be observed from the results presented in Table I,

that the quantifications are not conclusive influenced by the

time of ultrasonication, obtaining random results. These

confirm the fact that time increasing lead to the achieving of

an unstable and patchy adherence of the ionic liquid onto the

Florisil surface. On the other hand the increasing of the

ultrasonication amplitude lead to the increasing of the P, F,

and N quantifications. These indicate that the highest

quantity of the [BmimPF6] impregnated onto Florisil support

is obtained when the impregnation method through

ultrasonication is realized using an amplitude of 100% for 10

minutes. From these reasons we expect that the adsorbent

obtained in these conditions will develop the highest

efficiency in the removal process of Cs+ from aqueous

solutions.

Because from the SEM and EDX analyse was observed

that the ultrasonication time hasn’t a significant influence

onto the impregnation process, only the samples obtained at

various amplitude were submitted to the FTIR analyse. FTIR

the spectra of the used ionic liquid [BmimPF6], of the Florisil

and of the Florisil impregnated with the ionic liquid at

various amplitudes of ultrasonications are provided in Fig. 3.

In the IR spectra of these compounds are found of the

absorbtion bands from [BmimPF6] vibrational spectrum (the

bands between 2970-2850cm-1 are stretching vibration of

CH3 and CH2; the imidazolium CH stretching: 3125cm-1,

3177cm-1; the bands around 830cm-1 and 740cm-1 are

attributed to the antisymmetric respectively symmetric

stretching vibrations PF6 anion) [29]. The infrared spectra

show that the highest quantity of [BmimPF6] was

impregnated onto Florisil when 100% amplitude was used

(Fig. 3 g).

B. Adsorption of Cs+ from Aqueous Solutions

The results regarding the adsorption capacity of material

obtained at various work conditions of impregnation using a

S:L ratio of 0.1 g: 25 mL of 10 mg/L Cs+ solution are

presented in Fig. 4.

The obtained material through impregnation of Florisil

with the studied ionic liquid using various time of

ultrasonication developed random adsorption capacity in the

removal process of Cs+ ions from aqueous solution. It can be

notice that the increasing of the ultrasonication time did not

lead to an increasing of the adsorption performance of the

obtained material.

On the other hand the increasing of the amplitude of

ultrasonication in the process of Florisil impregnation with

the studied ionic liquid lead to the increasing of the

adsorption capacity of the obtained material. These results

confirm the fact that the removal of Cs+ ions from aqueous

solutions is dependent by the quantity of ionic liquid

impregnated onto the solid support. The results are in

agreement with the conclusions resulted from the analysis of

the impregnated materials. The most efficient adsorbent in


413

the removal process of Cs+ ions from a 10 mg/L solution

proved to be the Florisil impregnated with [BmimPF6] using

a 100% amplitude of ultrasonication for 10 minutes. This

material was treated with Cs+ aqueous solutions having

various concentrations (range: 5-50 mg/L) in order to

determine its maximum adsorption capacity. The adsorption

isotherm of Cs+ removal by the Florisil impregnated with

[BmimPF6] is presented in Fig. 5. It can be observed that the

initial removal of Cs+ is fast and at higher equilibrium

concentration the adsorption capacity achieve a constant

value.

Fig. 3. The FTIR spectra of the a) [Bmim PF6]; b) Florisil before

impregnation; c) Florisil impregnated at 10%; d) Florisil impregnated at 30%;

e) Florisil impregnated at 50%; f) Florisil impregnated at 70%; g) Florisil

impregnated at 100%.

The experimental data were fitted with Langmuir,

Freundlich, Temkin, and Dubinin-Radushkevich isotherm

models. The applying of Langmuir isotherm assume that

once an adsorbate molecule occupies a site no further

adsorption takes place and the forces of interaction between

adsorbed molecules are negligible. In case of the Freundlich

isotherm is assumed that the adsorption of the studied

adsorbate onto the surface of the adsorbent is heterogeneous

[9], [14], [19], [24]. Instead of Langmuir and Freundlich

isotherm was used the Temkin isotherm which take into

account the interaction between the adsorbent and Cs+ ions to

be absorbed being based on the free energy of adsorption as a

simply function of surface coverage [19], [28]. In order to

deduce the heterogeneity of the surface energies of

adsorption and the characteristic porosity of the adsorbent the

Dubinin-Radushkevich (D-R) isotherm model was applied to

the data [28].

Fig. 4. Adsorption capacity versus the ultrasonication work conditions.

Fig. 5. Cs+ adsorption isotherm onto the Florisil impregnated with

[BmimPF6].

The Langmuir constants (KL and qm) were obtained from

the slope and intercept of the plot of Ce/qe against Ce shown in

Fig. 6. The Freundlich constants (KF and 1/n) were obtained

from the plot of ln qe against lnCe (Fig. 7). From the slope

and intercept of the linear plot of qe against lnCe (Fig. 8)

were calculated the parameters of Temkin isotherm (KT and

bT). The constants of the D-R isotherm were obtained from

the plot and intercept of lnqe against [RTln(1+1/Ce)]2 (Fig. 9).

The constants of all isotherms and the regression coefficients

are presented in Table II.

Fig. 6. Langmuir plot of Cs+ adsorption onto Florisil impregnated with

[BmimPF6].

Fig. 7. Freundlich plot of Cs+ adsorption onto Florisil impregnated with

[BmimPF6].

Fig. 8. Temkin plot of Cs+ adsorption onto Florisil impregnated with

[BmimPF6].

Fig. 9. D-R plot of Cs+ adsorptiononto Florisil impregnated with [BmimPF6].

TABLE II: EQUILIBRIUM ISOTHERM PARAMETERS

Langmuir isotherm

qm exp, mg/g qm calc, mg/g KL, L/mg R2

1.47 1.6 0.24 0.9990

Freundlich isotherm

KF, mg/g 1/n R2

1.96 0.30 0.9063

Temkin isotherm

KT, L/g bT ΔG0 R2

3.63 8.26 -3.19 0.9624

D-R isotherm

qd, mg/g E, kJ/mol R2

1.36 14.2 0.9575

Comparing the isotherms applied, the Langmuir gave the

best fit, followed by the Temkin and Dubinin-Radushkevich

isotherms and then the least fit was obtained with the

Freundlich isotherm. It can be notice that the Langmuir

isotherm effectively describes the Cs+ adsorption onto the

studied adsorbent because is obtained a correlation

coefficient closed to unity. The low values obtained for the

Langmuir constant indicate that the Florisil impregnated with

[BmimPF6] has a high affinity for Cs+ ions. Also in this case

the obtained maximum adsorption capacity of the studied

adsorbent in the removal process of Cs+ ions from aqueous

solutions is closed with that experimentally obtained. An

important characteristic of the Langmuir isotherm is

expressed in a dimensionless constant equilibrium parameter

RL. The RL value indicates the shape of the isotherm and is

given in (7).

01

1

CKR

L

L

(7)

The obtained RL values are between 0 and 1 indicating a

favorable adsorption process. This suggests the applicability

of these adsorbents in the removal process of Cs+ ions from

aqueous solutions. One important characteristic of the

Freundlich isotherm is the 1/n parameter which is below one

indicating also a high affinity of the studied adsorbents for

the Cs+ ions. KT was used to determine the value of the Gibbs

free energy of adsorption as follows:

RT

GKT

0

exp (8)

The negative values of ∆G° confirmed the feasibility of the

process and the spontaneous nature of sorption. If the value

of the E is higher than 8 KJ/mol the sorption process is a

chemisorptions one, while values of below 8 KJ/mol

indicates a physical adsorption process. The value of the

apparent energy of adsorption obtained in this case indicates

chemisorption between the Florisil impregnated with

[BmimPF6] and Cs+ ions.


414


415

IV. CONCLUSIONS

The present paper showed that the work condition of

ultrasonication impregnation method is important in order to

enhance the adsorption capacities of the resulted adsorbents.

In order to obtain a stable and homogenous impregnation of

the solid support surface which will achieve reproducible

results in the adsorption processes it is not necessary to

increase the ultrasonication time, but we should use higher

amplitude. In this way the studied ionic liquid [BmimPF6]

adhered inside the cavities of the Florisil, not only at the

surface. Therefore the ultrasonication method is an efficient

method of impregnation because a shorter time and smaller

quantity of ionic liquids is used and the loss of the IL in the

aqueous phase is avoided. The impregnated material obtained

in the recommended conditions showed good adsorption

performance in the removal process of Cs+ from aqueous

solutions, developing a maximum adsorption capacity of 1.6

mg/g. The experimental data showed good fit to the

Langmuir isotherm, followed by the Temkin and

Dubinin-Radushkevich isotherms and then the least fit was

obtained with the Freundlich isotherm. The negative values

of ∆G° confirmed the feasibility of the process and the

spontaneous nature of sorption. The value of the apparent

energy of adsorption obtained indicates chemisorption

between the Florisil impregnated with [BmimPF6] and Cs+

ions.

ACKNOWLEDGMENT

This work was supported by a grant of the Romanian

National Authority for Scientific Research, CNCS –

UEFISCDI, project number PN-II-RU-TE-2012-3-0198.

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Lavinia Lupa was born on June 9, 1980 in Deva,

Romania. She is currently a lecturer at Faculty of

Industrial Chemistry and Environmental Engineering,

University Politehnica Timisoara, Romania. She has

obtained her PhD diploma in engineering science in

2008. Her teaching and research interests are in the

environmental engineering and waste waters treatment.

Adina Negrea was born on September 19, 1967 in

Hunedoara, Romania. She is currently an assistant

professor at Faculty of Industrial Chemistry and

Environmental Engineering, University Politehnica

Timisoara, Romania. She has obtained her PhD diploma

in engineering science in 2002. Her teaching and

research interests are in the environmental engineering

and waste waters treatment.

Mihaela Ciopec was born on October 8, 1977 in

Timisoara, Romania. She is currently a scientific

researcher at Faculty of Industrial Chemistry and

Environmental Engineering, University Politehnica

Timisoara, Romania. She has obtained her PhD

diploma in engineering science in 2008. Her teaching

and research interests are in the environmental

engineering and waste waters treatment.

Raluca Vodă was born on June 19, 1978. She is

currently a teaching assistant at Faculty of Industrial

Chemistry and Environmental Engineering, University

Politehnica Timisoara, Romania. She has obtained her

PhD diploma in Engineering Science in 2010. Her

teaching and research interests are in the inorganic

chemistry.

Petru Negrea was born on July 7, 1967 in Resita,

Romania. He is currently a professor at Faculty of

Industrial Chemistry and Environmental Engineering,

University Politehnica Timisoara, Romania. He has

obtained his PhD diploma in engineering science in

1996. His teaching and research interests are in the

chemical engineering and environmental protection.

studies regarding the influence of the ultrasonication conditions … · 2015-05-26 · with edax...

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